The present invention is related to U.S. Pat. No. 4,063,050 entitled "Acoustic Transducer with Improved Electret Assembly" issued to E. V. Carlson and M. C. Killion and assigned to the same assignee as the present invention. The disclosure of said patent is incorporated herein by reference.
The invention relates to an acoustic transducer of the type comprising an electret assembly including a diaphragm positioned adjacent a backplate having an electret film formed thereon. The electret assembly is mounted within a case to form acoustic chambers on opposite sides of the diaphragm. The case includes a channel for permitting the external acoustic signal to enter into one of the acoustic chambers to enable the diaphragm to respond thereto. Openings are provided to permit the air pulsations created by the vibrations of the diaphragm to pass from one to the other acoustic chamber.
The electret comprises a dielectric film deposited on a backplate. The backplate includes protrusions which rest on support posts formed in the case to selectively space the dielectric film from the diaphragm. The electret assembly including the diaphragm and backplate are conveniently mounted on support posts formed in the case. The diaphragm extends across the interior of the case and separates the case into essentially two chambers.
The electret dielectric film is connected to suitable electronic circuitry to thereby permit electroacoustical interaction of the diaphragm and electret to provide an electrical signal representative of the acoustic signal. As is known, the converse operation may be provided by the transducer in that an electrical signal may be applied to the electret to cause the diaphragm to vibrate and thereby develop an acoustic signal which can be coupled out of the acoustic chamber.